1. Field of the Invention
The present invention relates generally to a linear motion guide unit adapted for use in a variety of machinery such as semiconductor manufacturing machines, precision measuring instruments, precision inspection equipment, precision assembly machines or the like and, more particularly, to a linear motion guide unit that is provided therein with means for keeping a cage against wandering.
2. Description of the Prior Art
In recent years, linear motion guide units of the type hereinafter referred to as xe2x80x9cfinite linear motion guide unitxe2x80x9d because of their construction where rolling elements are allowed to roll over only a definite travel instead of rolling through a recirculating circuit have been used extensively in diverse fields of machinery such as semiconductor manufacturing machines to guide a part in a linear way relatively to any counterpart. Correspondingly, the finite linear motion guide units of the sort recited just above are seeing growing demands for high speed operation and high acceleration/deceleration, with even made slim or compact in construction. At the same time the advanced machinery expects the finite linear motion guide units to be operated with high precision and low-frictional resistance, and so on. Solving the issues stated earlier is needed for further development of the linear motion guide units.
Typically, most prior finite linear motion guide units of the type recited earlier have a mechanism for keeping a cage against wandering, which is a rack-and-pinion arrangement having, for example a rack 41 shown in FIG. 15. The rack 41 lies in a gutter for relief cut in a raceway groove of a guide rail member in a longitudinal direction thereof, with its tooth bottom part 44 coming into face-to-face contact with a gutter bottom 45. The rack 41 is slotted at 42 in such a fashion that the rack material remains on the tooth bottom part 44 between the slots 42 in the form of teeth 46 that are arranged successively in the lengthwise direction of the rack 41 at a pitch preselected to mesh with an associated pinion. Moreover, tooth tips 43 of the teeth 46 are made flat, for example as shown at 47. With the rack 41 constructed as stated earlier, the tooth bottom part 46 can contribute to keeping securely the teeth 46 at their desired positions. Nevertheless, modern tiny linear motion guide unit of the sort recited here can not frequently afford any space to allow the tooth bottom part 44 to have a thickness enough to hold up the teeth.
In Japanese Patent Laid-Open No. 108056/1999, there is disclosed a finite linear motion guide unit of the type recited earlier, which has means for keeping a cage or retainer against wandering to help control certainly the travel of finite guide rail members. The cylindrical rollers held in the cage are placed for rolling between confronting raceway grooves formed on the guide rail members. The cage has supported a pinion for rotation, which comes in mesh with a rack of gear teeth held in a gutter for relief. With the finite linear motion guide unit recited earlier, the rack lies in the gutter for relief cut lengthwise in the raceway groove formed on the guide rail member. The teeth on the rack are made recessed to avoid any interference with the cylindrical rollers. This construction allows the rack of gear teeth to be made in a module large in size, thus increasing the strength in mesh with the pinion thereby to keep the cage against wandering with respect to the associated guide rail members. Thus, the rack-and-pinion mechanism recited just above may be instrumental in keeping the cage against wandering relatively to the guide rail members.
The present assignee has already filed a senior pending Patent Application No. 2001-216235 in Japan relating a finite linear motion guide unit of the sort discussed here in which an earlier developed rack-and-pinion arrangement can serve effective function for keeping the cage against wandering. The finite linear motion guide unit discussed in the earlier pending application, although not shown here, is made shrunken in size and constructed such that a pinion coming into mesh with a rack is installed for rotation in a pinion holder fit in a cage. Especially, the senior application discloses means for keeping the cage against wandering, in which the pinion is held in a pinion chamber made in the pinion holder. The pinion is comprised of a disc having the teeth that are positioned circumferentially at regular intervals around the disc to form tooth spaces or slots each separating any two adjacent teeth, and a shaft carried in the pinion chamber for rotation to provide an axis about which the disc rotates. Moreover, the teeth formed around the disc are each made up of a dedendum part extending radially outwardly out of a curved periphery of the disc, and an addendum part integral with the dedendum part and made in a semicircular configuration. With the finite linear motion guide unit disclosed in the senior pending application, the rack lying lengthwise in the gutter for relief cut in the raceway groove on the guide rail member is made integral with the guide rail member by a molding process in which a powder of metal is formed with a metal injection molding, followed by being subjected to sintering.
With the every prior finite linear motion guide units of the sort discussed here, the rack is made with slots successive in the longitudinal direction thereof with the same pitch as the circular pitch of teeth on the mating pinion. The slots on the rack are each defined between two adjacent projections or teeth integral with a tooth bottom part and also designed to have a circular configuration somewhat larger in radius than the semicircular configuration of the addendum of the pinion tooth, thereby allowing the pinion making certain of sequential mating with the teeth on the pinion to smoothly come into successive mesh with the mating teeth of the rack. Moreover, the prior finite linear motion guide units of the sorts stated earlier, as the rack and the pinion are made relatively complicated in their tooth profile, are apt to encounter large sliding resistance and intermeshing resistance, and also very tough to shrink the guide unit itself down to tiny size in construction.
In most prior finite linear motion guide units of the sort discussed here, the guide rail member is commonly made on sides thereof with bolt holes lengthwise at preselected intervals, which are used to fasten the guide rail member to other object including a table, basement, sliding pedestal, machine bed and so on. When the linear motion guide units must meet an anticipated design demand to shrink them down as tiny as possible in size, nevertheless, the gutter for relief formed in the raceway groove on the guide rail member to fit the rack therein, just as in the conventional constructions, has to be inevitably restricted in depth to the extent where the gutter is allowed to extend around the fastening bolts. This makes the gutter for relief less in depth, thus making it tough to lay the conventional rack in the gutter.
The present invention, therefore, has as its primary object to overcome the major problems discussed earlier in the finite linear motion guide units of the sort stated earlier, and in particular to provide a finite linear motion guide unit with means for keeping a cage against any wandering, in which a rack has lengthwise side walls opposing widthwise across successive rack teeth to join the teeth together with one another so as to make it possible to keep the teeth between them at a preselected pitch even when any tooth bottom part does not necessarily remain in the rack. The present invention provides the finite linear motion guide unit with means for keeping a cage against wander, in which the tooth bottom part of the rack, if any, can be made as thin as possible to render the rack as slim as possible in depth. According to the present invention especially, the rack used in the means for keeping the cage against wandering is envisaged to fit snugly in the gutter for relief cut in the raceway groove to a depth where the rack is allowed to lie in the gutter for relief without any interference with bolt holes used to fasten a guide rail member to other object including a table, machine bed, sliding pedestal, and so on, and also the rack is held securely in the gutter by virtue of the side walls, which can make it possible to construct the linear motion guide unit itself as tiny as possible in size.
The present invention is concerned with a linear motion guide unit, comprising a pair of guide rail members that are arranged movable relatively to one another and have confronting raceway grooves on their lengthwise sides, one to each side, a cage retaining more than one rolling element allowed to run through in a raceway defined between the raceway grooves on the guide rail members, and means for keeping the cage against wandering; wherein the means for keeping the cage against wandering is comprised of racks lying in gutters cut in the raceway grooves, one to each raceway groove, in opposition to one another, and a pinion having teeth mating with the opposing racks and installed in the cage for rotation; and wherein the rack is composed of successive teeth spaced apart from each other at preselected intervals to allow the teeth to mesh with the pinion, and side walls extending in longitudinal direction on sidewise opposite sides of the teeth, one to each side, to connect the successive teeth together with one another.
In an aspect of the present invention, there is provided a linear motion guide unit in which the side walls of the rack come in engagement with surfaces defining the gutter cut in the raceway groove of the guide rail member thereby to keep the rack within the gutter in the raceway groove of the guide rail member. In another aspect of the present invention, a linear motion guide unit is disclosed in which the surfaces defining the gutter cut in the guide rail member lean away one another with depth while the side walls of the rack are rendered thickened sidewise with depth in a way conforming to the surfaces in the gutter. In another aspect of the present invention, a linear motion guide unit is disclosed in which the gutter in the guide rail member is cut in a fashion getting extended sidewise in the depths of the gutter to form a rectangular shape in traverse cross section, with any one side of the surfaces being set back in sidewise distance either identical with or different from another side, and the side walls of the rack are made thickened in a way conforming to the surfaces in the gutter. In another aspect of the present invention, a linear motion guide unit is disclosed in which the gutter is cut in the guide rail member to have the surfaces made concaved to bulge sidewise outwardly in the depths of the gutter, and the rack has the side walls each of which extends over an overall depth of the teeth and gets convex sidewise outwardly so as to conform to the associated surface of the gutter. In a further another aspect of the present invention, a linear motion guide unit is disclosed in which the gutter cut in the guide rail member has the surfaces made concaved sidewise outwardly at only deep area next to a bottom of the gutter, and the rack has side walls that are made thick at only limited area lower in the depth of the teeth so as to conform to the associated surface of the gutter.
In another aspect of the present invention, there is provided a linear motion guide unit in which the rack consists of only the teeth and the side walls integral with the teeth. As an alternative, a linear motion guide unit is provided in which the rack is made up of the teeth, the side walls and a tooth bottom part thin in thickness made integral with the teeth and the side walls.
In another aspect of the present invention, there is provided a linear motion guide unit in which the rack is made of either a resinous material or a low-temperature fusible metal, which is poured into the gutter of the guide rail member, then finished by removing partially material from the poured material with machining operations. As an alternative, a linear motion guide unit is disclosed in which the rack is kept in the gutter in the guide rail member, with the side walls being either close fit or fastened with adhesives in the gutter.
In another aspect of the present invention, there is provided a linear motion guide unit in which the side walls of the rack are made in a way coming into engagement with the surfaces defining the gutter cut in the guide rail member. In another aspect of the present invention, a linear motion guide unit is provided in which the teeth of the rack are rounded at their tooth tips. In a further another aspect of the present invention, a linear motion guide unit is provided in which the rack is made with a round slot between any two adjacent teeth, and the pinion has the teeth of round rods that extend radially outwardly and get spherical at their tooth tips so as to mesh well with the round slot of the rack. In another aspect of the present invention, a linear motion guide unit is provided in which the teeth of the rack are rounded at their tooth tips.
In a further another aspect of the present invention, there is provided a linear motion guide unit in which the rack is suitable for the use in a tiny linear motion guide unit where bolt holes used to fasten an object including a table, bed, base, sliding pedestal, machine bed, and so on to the guide rail member have to be in as close as possible to the bottom of the gutter on which the rack is laid.
With the linear motion guide unit constructed as stated earlier, the rack in the pinion-and-rack mechanism performing the duty of means for keeping the cage against wandering can shrink in size by constituting with at least only the successive teeth and the side walls. The tooth bottom part between any two adjacent teeth of the rack, if any, can be rendered in the form of film that has little thickness. According to the present invention, whether there is the tooth bottom part between any two adjoining teeth or not, the successive teeth are securely joined together with one another by virtue of only the side walls to be positioned firmly at preselected intervals that allow the teeth to mesh with the pinion. Thus, even though the gutter cut in the raceway groove on the guide rail member has to be restricted shallow in depth because of the bolt holes used to fasten the guide rail member to any other object, the rack can lie snugly, firmly in even the gutter less in depth and, therefore, suits the tiny guide rail member.
As the rack constructed as stated earlier is adaptable for the rack in the rack-and-pinion arrangement that may serve as the means for preventing the cage from any wandering in the linear motion guide unit disclosed in the senior pending Japanese Patent Application No. 2001-216235, the finite linear motion guide unit with rack according to the present invention makes it possible to use the pinion in the pinion-and-rack arrangement just as it is. Moreover, the finite linear motion guide unit with the rack of the present invention is applicable well for a wide ranges of sizes, from very small to very large guide rail members, also helping make certain of the accurate linear travel of the moving part such as a table, meeting demands for high speed operation and high acceleration/deceleration of the moving part or the table, with even made slim or compact in construction, and at the same time helping serve useful functions such as low-frictional sliding resistance, and so on.
The rack incorporated in the finite linear motion guide unit of the present invention, because the successive teeth lying in lengthwise direction are joined together with at least only the side walls, can be made reduced in depth to allow the rack to fit snugly, firmly in even the gutter that is cut shallow in the raceway groove of the guide rail member lest the gutter comes into no interference with the bolt holes used to fasten a guide rail member to other object. With the rack in the present invention, moreover, the successive teeth can be connected to one another with only the side walls so as to take on the function of the rack even though the tooth bottom part has little or no thickness.
Accordingly, the linear motion guide unit with the rack constructed as stated earlier is suitable for the small instruments including semiconductor manufacturing machines, precision machines, and so on. The pinion-and-rack arrangement constituting the means for keeping the cage against any wandering may be installed in the cage easily with accuracy by only close-fit of the arrangement in an aperture cut in the cage. Moreover, the linear motion guide unit of the present invention is preferable for the small machines, and also helps make certain of the accurate travel of the moving part such as a table mounted on any guide rail member, meeting demands for high speed operation and high acceleration/deceleration of the moving part or the table, with even made slim or compact in construction. At the same time the present invention helps serve useful functions such as low-frictional sliding resistance, and so on anticipated for linear motion guide unit of the sort discussed here.
Other aspects, objects and advantages of the present invention can be obtained from a study of the drawings, the disclosure and the appended claims.